The ingestion of mind altering substances is very nearly a human universal ; in practically every society, a sizeable proportion of its members take at least one drug for psychoactive purposes. This has been true for a significant stretch of history. Fermentation was one of the earliest of discoveries, predating the fashioning of metal; humans have been ingesting alcoholic bevarages for more than 10,000 years. Several dozen plants contain chemicals that influence the workings of mind, and have been smoked , chewed or sniffed by members of society all over the world. These plants include coca leaves, the opium poppy, marijuana, the psilocybin mushroom, the peyote cactus , quat leaves, nutmeg, tobacco, coffee beans, tea leaves and the cocoa beans. During the past century or more hundreds or thousands of psychoactive substances have been discovered. Isolated or synthesized by scientists or physicians.
Thousands have been marketed for medicinal purposes. How ever these days in a significant majority of cases drugs are taken in a culturally unacceptable or disaproved fashion : a condemned drug is taken instead of an aproved one. It is taken too frequently or under the wrong circumstances, for wrong reasons, or with undesirable consequences. It must be emphasized that drug use is not a unitary phenomenon. There are, to begin with different types of drugs classified according to their action. Drugs are commonly categorized according to their action on the central nervous system - the brain and spinal cord. Some drugs speed up signals passing through the CNS; they are called stimulants and include cocaine, the amphetamines, caffeine and nictine. Other drugs retard signals passing through the CNS and are called depressants include narcotics ( such as heroin , morphine , opium ), which dull the sensation of pain, sedatives ( such as alcohol , the barbiturates and methaqualone ) and minor tranquillizers ( such as Valium), which reduce anxiety and major tranquillizers or anti psychotics, which inhibit the manifestation of symptoms of psychosis, especially schizophrenia. Hallucinogens ( such as LSD ) and marijuana do not fit neatly into this stimulant-depressant continuum.
Psychoactive drugs even of the same type are taken for a variety of reasons to attain religious or mystical ecstacy, to suppress fatigue, hunger or anxiety, to enhance hedonism and pleasure, to heal the body or the mind, to facilitate socialising or interpersonal intimacy, to follow the dictates of a particular group or subculture, and to establish an identity as a certain kind of person. A drug's psychactive properties may be central to the user's psychoactive properties may be central to the user's motive for taking it, or incidental to it the intoxication may be intrinsic reasons or the drug taken for instruemental purposes.
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